High Pressure Gates and Valves
Article 61. Outline of Design
. Taking into account the failure and repair of the high pressure outlet
equipment, at least two high pressure gates or valves, a main and an auxiliary, shall be provided.
. The high pressure outlet equipment shall be so structured as to be rigid,
and durable for long use and shall ensure easy maintenance.
. Materials used shall have good anti-wear and anti-cavitation proper
ties depending on the water head.
Description:
The high pressure outlet equipment can cause great damage should an accident occur and cavitation and vibration may take place. Therefore, it is necessary to refer to the Description of Article 12. of this Chapter for allowable stress and to refer to the Descriptions of Article 17. and Article 18. for coefficient of friction. The larger figure should be adopted.
Generally, high tensile steel is not used and rigidity should’be increased by using mild steel even though the weight increases somewhat.
Stainless steel is generally used for the part which requires cavitation resistance and wear resistance.
Article 62. Shape of the High Pressure Gate
It should be noted that the shape and structure of the passage, the gate leaf and the gate guide highly influence vibration and cavitation of the leaf.
* ,
Description:
The high pressure gate herein is a hydraulic gate for discharging water installed at a location higher than a 25m waterhead. The high pressure gate of an orifice type and valve (less than 25m waterhead) should be in accordance with the provisions of this Article depending on the type of gate.' .
The characteristics of high pressure gates for various outlet equipment are listed in Table 2.62-1.
By referring to the Description of Article 16., this Chapter for lip of gate leaf and to the Description of Article 64., this Chapter for passage and gate guide, attention should be paid to these shapes and structures. It is desirable to run a model test and then select an appropriate shape especially in case of a high pressure or special shape.
Type
.
Installation
location
Coefficient
of discharge
Upstream
end
Middle
Downstream
end
Ring
seal gate
O
1.00
Ring
follower gate
O
1.00
Slide
gate
Q
0
0.94-0.97
Radial
gate
•
0
1.00
Jet
flow gate
o
•0
0.80-0.84
Fixed
wheel gate
O
O
1.00
Caterpillar
gate
O
0
1.00
Table
2.62-1
Mark O shows applicable ones.
Mark 0 shows those capable of partial discharging.
Article 63. High Pressure Valve
The type of high pressure valve shall be selected by taking account of7 the water discharging characteristics, the loss of head, the cavitation characteristics, etc.
Description’.
Type
Installation
location
Coefficient
of discharge
Middle
Downstream
Gate
valve
O
Butterfly
valve
O
Rotary
valve
O
—
Hollow
jet valve
0
0.70—0.85
Cone
valve
0
0.85
Cone
sleeve valve
0
0.73
Table
2.63-1 Characteristics of High Pressure Valves for Various Outlet
Equipment
Article 64. Shape of Passage
. The gate groove shall be so shaped as to prevent the rapid flow penetra
tion as much as possible.
. Passage surfaces contacting a high velocity flow* shall be sufficiently
smooth and the shape shall not adversely affect the flowing water.
. Water inside the passage must not flow into the control room.
Description:
Since the gate groove disturbs the flow, extreme care should be taken in designing this item for high pressure flow. When it is installed in the middle of a passage, structures as illustrated in Fig. 2.64-1 have been employed:
Flow
Ring
follower
(1)
Coefficient of discharge Co
*
1.00
Gate
groove
(2)
Coefficient of discharge
CD
= 0.80-0.84
~
Flow
Gate
groove
Flow
/
^Pprox.
/50
Offset
0.075^-0.10^
(3)
Coefficient of discharge Cn
= 0.80-0.84
(4)
Coefficient of discharge CD
= 0.94-0.97
Fig, 2.64-1 Shape of Gate Groove
bio: 1
